Plate-type heat exchanger



p 30, 1969 s. RAWLINGS 3,469,623

PLATE-TYPE HEAT EXCHANGER Filed Oct. 25. 1967 United States Patent U.S. Cl. 165-70 4 Claims ABSTRACT OF THE DISCLOSURE A plate-type heat exchanger in which the plates are provided by parallel portions of a plurality of tubes, the tubes being arranged in sets and in each set an inner tube is disposed within an outer tube, the inner tubes of the sets defining within them passages of a first group While passages of a second group are defined between the inner and outer tubes of the sets.

BACKGROUND OF THE INVENTION Field of the invention.This invention relates to heat exchangers of the plate-type in which spaced-apart plates are provided to form passageways for fluid.

Description of prior art.In conventional plate-type heat exchangers, plates are spaced-apart by spacer bars which are of extruded or machined section. The use of these spacer bars is expensive and adds to the cost and inconvenience in manufacture of the exchangers. It would be advantageous, therefore, it a plate-type heat exchanger could be provided which eliminated the need for extruded or machined section spacer bars and which, in consequence, could be made lighter in construction than the conventional exchanger.

SUMMARY OF THE INVENTION According to the invention, a plate-type heat exchanger has a plurality of tubes, each having opposed parallel portions to form plates of the exchanger, the tubes being located in a plurality of superposed sets with each set comprising two tubes, one disposed within the other with the inner tubes of the sets bordering a first group of passages and with the inner and outer tubes defining between them a second group of passages.

It is preferable if, in each set of tubes, the inner tube is completely spaced from the outer tube so that each passage of the second group completely surrounds a passage of the first group when considered in end view of the tubes.

In one preferred construction, adjacent sets of tubes are spaced-apart to provide between them a third group of passages. In this construction, the first and third groups of passages may be used, respectively, for conveying first and second fluids through the exchanger for heat exchange purposes. Passages of the second group as they completely surround passages of the first group effect, therefore, complete spacing apart of the passages of the first and third groups and may be used to act as leakage passages for the leakage of fluid from either of the first and third groups so as to prevent mixture of the fluids in the event of failure of one of the tubes. This construction is particularly useful under certain conditions of operation as aircraft heat exchangers, in which leakage which might allow a possible mixing of the two fluids, may be dangerous and, in any case, leads to wastage of one of the fluids. As an example of this, the heat exchanger, if used as a fuel preheater for an aircraft will have fuel as one of the fluids. If leakage of the fuel occurs, this leads to wastage of fuel but there is also at- 3,469,623 Patented Sept. 30, 1969 ice tendant fire risk because of the mixing of the fuel with the heating fluid.

In an alternative construction, only the first and second groups of passages are employed and the sets of tubes are disposed one directly above another with the passages of the first and second groups being provided, respectively, for conveying first and second heat exchanger fluids.

BRIEF DESCRIPTION OF THE DRAWING One embodiment of the invention will now be described by way of example, with reference to the accompanying drawing, which is an isometric view, partly cut away, of a plate-type heat exchanger with certain header tanks removed for clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGURE 1, an aircraft plate-type heat exchanger for preheating fuel comprises a plurality of tubes 1 and 2, each tube having opposed parallel portions to provide plates 3 of the exchanger. Each tube is made from a metal sheet, the sides of which are overlapped and brazed or soldered together. The tubes 2 in crosssection are smaller in circumferential length than the tubes 1 and the tubes are arranged in spaced-apart superposed sets, each set comprising a tube 2 surrounded by a tube 1. The tubes 2 are completely separated from their associated tubes 1 by corrugated metal sheet 4 so that an annular leakage passage 5 for fluid is provided between the two tubes of each set, all of the passages 5 forming a group of leakage passages. Each of the tubes 2 borders one of a group of passages 6 for conveying a first heat exchange fluid which is fuel, corrugated metal sheets 7 being provided within the passages 6 to form secondary heat exchange surfaces.

The ends of passages 6 communicate with header tanks, the base plate 8 of one of the header tanks being shown. Each base plate is formed from a pressing of metal in which flanged holes 9, complementary to the outer surface of the tubes 2, are provided for surrounding the ends of the tubes 2 and to which the ends of the tubes are fluidtightly secured by known brazing or soldering techniques. Each plate 8 has portions 10 of substantially semi-circular cross-section at the sides of the holes 9, so as to add strength to the plate to resist deformation caused by pressure of fluid passing through the exchanger. A continuous bordering flange 11 is provided for each plate, the flange being fluid-tightly secured to side plates 12 provided one on each side of the exchanger. A header tank shell (not shown) is secured in known manner to each plate 8 to define a header chamber for containing the first fluid.

As shown in the drawing, the tubes 1 terminate short of the ends of the tubes 2 and at each end the tubes 1 are secured within holes 13 of a plate 14 of similar shape to the header plate 8-. Each plate 14 is spaced-apart from its adjacent plate 8 to provide subsidiary passages 15 between the two plates and into which the group of passages 5 extend. Semi-circular portions 16 of the plate 14 lie between the spaced-apart sets of tubes to assist in holding them in position. The subsidiary passages 15 enter at their ends into subsidiary header tanks 17 which are disposed at the corners of the heat exchanger.

Sheets 18 of corrugated metal are located between the spaced-apart sets of tubes and between each of the side plates 12 and the adjacent set of tubes to provide secondary heat exchange surfaces of a group of passages 19 for flow of a fuel heating fluid in a direction transversely to the direction of flow of the fuel within the passages 6. Header tanks (not shown) are fluid-tightly secured to the ends 20 of the exchanger for the heating fluid.

In use of the exchanger, while the fuel and the heating fluid flow along the passages 6 and 19', if one of the tubes fails and allows for leakage of one of the fluids, this fluid will flow directly either into one of the leakage passages 5 or into one of the subsidiary passages 15, eventually to flow into a header tank 17. Upon the fluid reaching the header tank 17, fluid responsive means operate in known manner to provide a warning signal to the aircraft pilot that failure of the heat exchanger has occurred.

In use of the construction, therefore, if, as in the present instance, two fluids which are passing through the heat exchanger are such that it would be undesirable to allow for mixing of the fluids for safety or other reasons, leakage of either of the fluids will now allow for their mixing and, before a further failure takes place in the exchanger, operation of the exchanger may be stopped.

It is interesting to note that because of the provision of the sets of tubes and passages 15, each of the passages 6 is completely spaced by leakage passages from the passages 19 and the header tanks located at the ends 20 of the exchanger, while the passages 19 are separated by leakage passages from the fuel header tanks. Further, because the heat exchanger is made with the tubular construction, it may be lighter and more convenient and economical to make than conventional plate-type heat exchangers in which plates are spaced-apart by extruded or machined metal spacer bars located along the edges of the plates. The cheapness of the assembly is further assisted by the pressed steel construction of the plates 8 and 14 which also replace the spacer bars normally used on plate-type heat exchanger assemblies.

In a modification of the construction described above, however, spacer bars may be used instead of the plates 8 and 14 to form the subsidiary passages 15 and provide a base for the header for the fuel. Such a construction, however, although incorporating the tube construction would not be as convenient and economical to make and would be slightly heavier than the construction described in the embodiment.

I claim:

1. A plate-type heat exchanger having a first and second group of passages wherein the improvement is comprised in that the exchanger has a plurality of tubes, each tube being formed from sheet metal and having opposed flattened and parallel portions which are parts of the same metal sheet and form plates of the exchanger, parts of each tube extending between the flattened portions to space said portions apart and each part being integral with at least one of the flattened portions, the tubes being located in a plurality of superposed sets with each set comprising an inner tube and an outer tube, with the inner tube disposed within the outer tube, the inner tubes defining within them the passages of the first group, and the inner and outer tubes defining between them to passages of the second group, each inner and outer tube having inlet and outlet ends for fluids, and the passages extending along the tubes from end to end.

2. A plate-type heat exchanger having a first second and third groups of passages wherein the improvement is comprised in that the exchanger has a plurality of tubes, each tube being formed from sheet metal and having opposed flattened and parallel portions which are parts of the same metal sheet and form plates of the exchanger, parts of each tube extending between the flattened portions to space said portions apart and each part being integral with at least one of the flattened portions, the tubes being located in a plurality of spaced-apart and superposed sets with each set comprising an inner tube and an outer tube with the inner tube disposed within the outer tube, the inner tubes of the sets defining within them the passages of the first group for flow therethrough of a first fluid and the spaced-apart outer tubes of the sets defining between them the passages of the third group for flow therethrough of a second fluid, the inner tubes having two ends which provide inlet and outlet ends of the first group of passages and the spaced-apart outer tubes providing between them inlet and outlet ends of the third group of passages, and the inner and outer tubes of each set defining between them a passage of the second group, passages of the second group being leakage passages for leakage of fluid from passages of either of the first or third groups, the outer tube of each set having two ends, both of which together with an outer surface of the inner tube define outlet ends for the passage of the second group of that set of tubes.

3. An exchanger according to claim 2 wherein in each set of tubes, the inner tube is completely spaced from the outer tube so that the passage of the second group defined between the inner and outer tubes completely surrounds the associated passage of the first group when considered in end view of the tubes.

4. An exchanger according to claim 3 wherein the third group of passages extend transversely to the direction in which the first and second groups extend, the third group is provided at each end of its passages with a header tank which is spaced from passages of the first group by the second group of passages, the first group of passages is provided with header tanks at the ends of the inner tubes, and subsidiary passages for the leakage passages are disposed between the header tanks of the first group of passages and the third group of passages.

References Cited UNITED STATES PATENTS 2,846,198 8/1958 Sturges -167 X FOREIGN PATENTS 1,088,027 9/ 1960 Germany.

ROBERT A. OLEARY, Primary Examiner T. W. STREULE, Assistant Examiner U.S. Cl. X.R. 165-l66 

